Pianist

As a pianist, Koppel premiered in 1930 at a concert where he included Carl Nielsen's Opus 40, "Theme with Variations", which was enthusiastically acclaimed as "never having been played so beautifully as this evening". Shortly before Nielsen's death in 1931, Koppel performed a concert dedicated to his music, first playing the pieces for Nielsen himself. Thereafter, throughout his life, Koppel continued to perform Nielsen's compositions.^[4]

In addition to Nielsen's music, Koppel's repertoire included romantic pieces, especially those by Mozart and Brahms. He also frequently played more modern music from a variety of composers, including the concertos of Bartok, Hans Werner Henze and Darius Milhaud and pieces by Stravinsky and Arnold Schönberg. Koppel played chamber music in the Koppel Quartet and accompanied singers including Aksel Schiøtz and his daughter Lone Koppel.^[4]

Composer

As a composer he was self-taught. His début composition was a string quartet (1928–29) which, like his other early works, was inspired by Nielsen and Stravinsky. The first work in his own style was his Piano Concerto No. 1 in March 1933, with its primitive Russian dance rhythms and Afro-American jazz. Koppel himself preferred his Piano Concerto No. 2 (1938) while No. 3 (1948) is Denmark's most popular piano concerto and one of the few to be published as a recording.^[4]

Only a few of the works he wrote in the 1930s have survived. The most important is the jazz-inspired music he wrote together with Bernhard Christensen for Kjeld Abell's musical comedy Melodien der blev væk (The Melody That Got Lost) premiered in 1935. During the German occupation of Denmark in the Second World War, Koppel, together with his wife and two small children, had to move to Sweden.^[6] It was there he wrote his Symphony No. 3. His Tre Davidssalmer (1950) was inspired by an episode he witnessed during the war when a group of Jews locked inside a German truck began to sing slowly and softly.^[4]

Koppel wrote seven symphonies, his fifth winning the Tivoli competition in 1956.^[7] His most successful works are his oratorios: Moses (1964), Requiem (1966) and Lovsange (1973). His only opera Macbeth, performed at the Royal Danish Theatre in 1970, was less successful, receiving mixed reviews. As for his chamber music, the most often performed are his Sekstet for klaver og blæsere (1942) and Ternio for cello and piano (1951). Koppel also wrote music for 29 films and several stage and radio plays. He continued to compose and perform until the mid-1990.^[4][6]

Orchestral works

• Symphony No. 1 (1931) Op. 5
• Symphony No. 2 (1943) Op. 37
• Symphony No. 3 Op. 39 (1944–45)
• Symphony No. 4 Op. 42 (1946)
• Symphony No. 5 Op. 60 (1955)
• Symphony No. 6 (1957) Sinfonia Breve Op. 63
• Symphony No. 7 (1960–61) Op.70
• Music for Strings (1930)
• Music for Jazz Orchestra (1932)
• Variations for Small Orchestra (1935)
• Festival Overture (1939)
• Concertino No. 1, for String Orchestra (1937–38)
• Concertino No. 2, for String Orchestra (1957)
• Sinfonietta (1945)
• Concerto for Orchestra (1977–78) Op. 101
• Intrada (1979)
• Prelude to a Symphony, Op. 105 (1979)
• I Dis og Drøm (1992) String Orchestra
• Memory (1994) String Orchestra

Works for solo instrument and orchestra/ensemble

• Piano Concerto No. 1 (1931–32)
• Piano Concerto No. 2 Op. 30 (1936–37)
• Piano Concerto No. 3 Op. 45 (1948)
• Piano Concerto No. 4 (1960–63)
• Violin Concerto (1929)
• Capriccio for violin and orchestra (1934)
• Clarinet Concerto Op. 35 (1941)
• Double Concerto for Violin, Viola and Orchestra Op. 43 (1947)
• Cello Concerto Op. 56 (1952–56)
• Oboe Concerto (1970)
• Chamber Concerto for Violin and String Orchestar (1970)
• Flute Concerto Op. 87 (1971)
• 8 Variations and Epilogue, for piano and orchestra (1972)
• Triple Concertino, for string trio and orchestra (1983)

Chamber works

• String Quartet no.1 (1928–29)
• String Quartet no.2 (1939) Op. 34
• String Quartet no.3 (1944–45) Op. 38
• String Quartet no.4 (1964)
• String Quartet no.5 (1975)
• String Quartet no.6 (1979)
• Duo pour violon et piano (1930)
• Trio pour clarinette, violon et piano (1931)
• Sonatine for Wind Quintet (1932)
• Variations on a Jewish folk dance vl, vla, vlc (1932)
• Duo pour clarinette et basson (1932)
• 11 variationer over eget tema [11 Variations on a theme of my own] fl, vl, vla, vlc (1935)
• Suite fl, vl, vlc (1936)
• Sextuor pour instruments à vent et piano Op. 36 (1942)
• Fantaisie pour clarinette seule (1947)
• Ternio I pour violoncelle et violon et piano Op. 53b (1951)
• Quintette avec piano Op. 57 (1953)
• Divertimento Pastorale ob, vla, vlc (1955)
• Sonate pour violoncelle et piano Op. 62 (1956)
• Variations pour clarinette et piano (1961)
• Capriccio pour flûte et piano (1961)
• 9 variations pno, vl, vlc (1969)
• 4 improvisationer [4 Improvisations] fl, vlc (1970)
• Suite pour violoncelle seul Op. 86 (1971)
• Koncert for fløjte og orkester [Concerto for Flute and Orchestra] Flute and Piano (1971)
• Trio pno, vl, vlc Op. 88 (1971)
• 8 variations et epiloque pour piano et 13 instrumentistes (1972)
• Divertimento pour trio à cordes (1972)
• Ternio II pour saxophone seul (1973)
• Variazioni Pastorale fl, vl, vla, vlc (1975)
• Variazoni libre 2 cl, Bcl, perc (1976)
• Dialog Tema med variarioner og monolog for fløjtesolo [Dialogue] Flute solo (1977)
• Patch-work fl, arpa, vla (1981)
• Quartet pno, vl, vla, vlc (1986)
• Trio cl, pno, vlc (1986)
• Cantilena Duo vl, vlc (1988)
• Musik for Blæseroktet [Music for Wind Octet] Wind Octet Op. 123 (1991)
• Musik for violin og klaver [Music for violin and Piano] Violin and Piano (1991)
• Giocattolo fl, cl, perc, pno, vlc (1993)

Works for piano

• Piano Sonata E minor, op. 1, 1928
• Variations and Fugue for Piano, op. 3, 1929
• Piano Piece, op. 7, 1930
• Suite for Klavier [Suite for Piano] Op. 21 (1934)
• Sonata no. 1 for Piano, op. 50, 1950
• 15 miniaturer [15 Miniatures] op. 97a (1976)